The present invention relates to a combination of a fuel injection valve having a single fuel injection hole and a nozzle, and more particularly to an improved structure of a nozzle which is designed to improve fuel atomization, especially for use with an engine having a single intake valve per cylinder.
Generally, an engine having a single intake valve per cylinder employs a pintle type injection valve having fuel atomization and emission characteristics better than a single hole type injection valve. However, the fuel deposit property of the pintle type injection valve is inferior to that of the single hole type injection valve because of the valve structure of the former, causing blocking of the fuel injection hole and accordingly reducing the flow of fuel. On the other hand, since the single hole type injection valve injects fuel columnarly and not in a conical shape, satisfactory atomization of the fuel cannot be obtained, and the formation characteristics of the air/fuel mixture is inferior to that of the pintle type injection valve. Especially when the atomization is not sufficient under cold engine condition, the amount of HC emission is increased, and as a result, the feedback control characteristic is deteriorated causing an increase in unburnt components other than HC.
There are described some countermeasures against the above problems in Japanese Utility Model Laid-Open Publication No. 57-152458, wherein an atomizing adapter is located downstream of a single hole type fuel injection valve, so as to prevent the blocking of the injection aperture caused by the fuel deposition and coincidently to provide a fuel atomization characteristic equal to or higher than a pintle type fuel injection valve. However, it is difficult in actual manufacturing to locate such an obstacle adapter downstream of a small fuel injection hole in coaxial relationship therewith.
In the case of mounting the prior art injection valve just above an intake valve in an intake manifold of an engine, the atomized fuel cannot be effectively supplied to the engine without the deposition of the fuel onto a wall surface of the intake manifold, or by the prior art injection valve, the fuel pressure at the fuel injection hole does not change equally to the intake manifold pressure. Therefore, accurate fuel metering cannot be achieved unless some characteristics required to the valve mentioned above are satisfied. Thus, the prior art has not yet solved the problems in fuel deposition property, fuel atomization characteristic, fuel metering characteristic and coincidently productivity.